One of known brake apparatus for a vehicle is provided with a master cylinder, each wheel brake cylinder respectively mounted on each vehicle wheel, and a recirculating type hydraulic pressure modulator. The master cylinder outputs to the wheel brake cylinder a hydraulic pressure corresponding to an operating force inputted to the master cylinder from a side of a brake pedal. The wheel brake cylinder applies to the vehicle wheel a brake torque corresponding to the hydraulic pressure inputted to the wheel brake cylinder. The recirculating type hydraulic pressure modulator is disposed in a hydraulic pressure conduit connecting the master cylinder and the wheel brake cylinder so as to modulate the hydraulic pressure in the wheel brake cylinder to be different from the hydraulic pressure outputted from the master cylinder.
The recirculating type hydraulic pressure modulator is one of the components of an anti-lock control device and is provided with an auxiliary reservoir, a normally open type electromagnetic switching valve (hereinafter, referred to as a normally open type valve), a normally closed type electromagnetic switching valve (hereinafter, referred to as a normally closed type valve), a recirculating pump, and an electric motor for driving the recirculating pump. The normally open type valve serves for interrupting a communication between the master cylinder and the wheel brake cylinder. The normally closed type valve serves for establishing a communication between the wheel brake cylinder and the auxiliary reservoir. The recirculating pump serves for recirculating a brake fluid accumulated in the auxiliary reservoir to a hydraulic pressure conduit between the master cylinder and the normally open type valve.
However, the above described vehicle brake apparatus may have a following problem. An insufficient sealing of the normally closed type valve may occur due to a foreign object between a valve body of the normally closed type valve and a valve seat thereof. In this case, upon an operation of the brake pedal, the brake fluid sent to the wheel brake cylinder from the master cylinder may be leaked to the auxiliary reservoir due to the insufficient sealing of the normally closed type valve. Therefore, a brake pedal stroke amount under the above described condition may be drastically increased for obtaining a desired vehicle wheel brake torque comparing with a brake pedal stroke amount under a normal sealing condition of the normally closed type valve. In other words, when the brake pedal is operated in the state where the normally closed type valve raises insufficient sealing, the desired vehicle wheel brake torque may not be obtained.
Accordingly, the above disclosed vehicle brake apparatus is still susceptible of certain improvements with respect to restraining an increase of the brake pedal stroke amount due to the insufficient sealing of the normally closed type valve of the recirculating type hydraulic pressure modulator.
Further, the other known brake apparatus is additionally provided, for example with a fluid pressure type booster. The fluid pressure type booster boosts the operating force applied to the brake pedal and inputs the boosted operating force to the master cylinder. When the fluid pressure type booster malfunctions, the brake pedal operating force is drastically increased so as to obtain the desired vehicle wheel brake torque comparing with the brake pedal operating force under the normal boosting condition of the fluid pressure type booster. Therefore, should the driver apply a normal operating force to the brake pedal when the insufficient sealing is raised by the normally closed type valve and when the fluid pressure type booster malfunctions, the brake pedal stroke amount will not be sufficiently large for obtaining the desired vehicle wheel brake torque.
Accordingly, the above disclosed vehicle brake apparatus is still susceptible of certain improvements with respect to restraining the increase of the brake pedal stroke amount relative to the normal brake pedal stroke amount when the fluid pressure type booster malfunctions and when the insufficient sealing is raised by the normally closed type valve.